Milk provides an environment that is particularly favorable for the growth of microorganisms, resulting in the rapid growth of mold, yeast and bacteria. Milk that is freshly drawn is around 38 degrees Celsius and needs to be cooled to 16 degrees to reduce bacterial growth and retard enzyme activity.
Milk is also cooled quickly to prevent natural souring, ensuring the milk keeps longer. Milk is sometimes allowed to naturally sour to make other products, such as yogurt, sour cream and cheese. The process of pasteurization is frequently used to remove bacteria from milk by heating the milk to 72 degrees Celsius for a short time, followed by rapid cooling to below 10 degrees.